As a method for mounting a semiconductor chip onto a substrate, a method referred to as flip-chip mounting has been widely adopted. In the case of flip-chip mounting, a body provided with several conductive bumps, that is, bumps usually made of gold, serving as connecting terminals is placed face down onto the surface (referred to as main surface, hereinafter) where circuits are formed on a semiconductor chip, that is, with the main surface facing the substrate, in order to bond said conductive bumps directly to the wires on the substrate. In flip-chip mounting, a method referred to as ultrasonic thermocompression bonding has long been well known as a method for bonding said conductive bumps to the wires on the substrate.
In the ultrasonic thermocompression bonding method, a semiconductor chip is held by suction using a vacuum suction tool and placed over the area where the bumps are to be mounted onto the wires formed on the substrate. When bonding the gold bumps onto the wires, a fixed amount of pressure is applied to the semiconductor chip using a suction tool, and the substrate is heated at the same time. Under said conditions, ultrasonic vibrations of a prescribed frequency are applied to the semiconductor chip via said suction tool. The gold bumps on the semiconductor chip are well bonded to lands on the substrate by said pressure, heat, and ultrasonic vibrations.
In order to transmit the energy of the ultrasonic vibrations applied via said suction tool to the conductive bumps efficiently, it is important to bring the suction tool and the semiconductor chip into close contact by means of vacuum suction. However, a minute gap may be created between the suction surface of the suction tool and the back of the semiconductor chip placed against the suction surface, resulting in a drop in suction power. This drop in suction power not only reduces the energy of the ultrasonic vibrations applied to the gold bumps but also creates another problem.
That is, when the suction power of the suction tool drops, the semiconductor chip can no longer follow the ultrasonic vibrations applied to the tool, resulting in the problem that tip of the suction tool ends up abrading the surface of the semiconductor chip due to friction. Some of the scraped-off fine silicon particles stick to the back of the semiconductor chip, land on the substrate, and may even be incorporated into a device eventually.
In addition, even when the aforementioned drop in the suction power is not present, the semiconductor chip stops following the vibrations of the suction tool when or immediately before the conductive bumps become fixed to the wires on the substrate. In such case, also, the aforementioned problem of chip abrading occurs.
The particles stuck to the semiconductor chip have potential for causing serious problems depending on the ultimate use of the semiconductor chip. For example, a preamplifier bare chip to be mounted on an actuator in a hard disk device may be mentioned. Said scraped-off particles (they are 0.1-5 .mu.m or so in size) stuck to the semiconductor chip come loose inside the device due to vibrations caused by revolution of the magnetic disk and ultimately fall onto the disk. Because the magnetic head floats at a distance of 50 .mu.m or less from the disk surface, said scraped-off particles on the disk seriously affect the function of the hard disk drive.
Therefore, the purpose of the present invention is to prevent said problems caused by said abraded particles when mounting said semiconductor chip, by preventing creation of the particles by abrasion of the chip while it is being mounted onto the substrate using the ultrasonic thermocompression bonding method.